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What'd you folks do with the CTS in your renix to HO swap

M

Mike1331

NAXJA Forum User
Location
Folsom, CA
I'm stuck with this last thing, my renix head and my 93 head that i swapped onto my renix block both had a hole drilled in the back to acomidate one of the cts's. I'm swapping in a 99 motor with the 0630 head and it doesn't have a hole drilled in the back for the cts. They moved it to the thermo housing. I spent a good hour in the hardware store looking for adapters/reducer and the like to try and get a ho thermo housing to accept my renix cts. I couldn't find one. Could someone please post a pic of how they made the renix cts work on the ho thermo housing? Or whatever you did to make it work?? I don't want to drill and tap a hole in my head. I'm running out of budget and i don't want to spend any more money on a pipe tap.

Thanks to any and all for help.
 
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Um, try and splice the current wire for CTS into the one on the t-stat housing.
 
You'll want a buching to reduce 3/8" NPT to 1/8" NPT. If you can't find that at a hardware store, see if you can't find it at a plumbing shop.

Of course, you're going to see a slightly reduced reading - the rear of the cylinder head is pretty much the hottest spot in the cooling system, while you're going to have nice flow over the thermostat area.

You can probably make a pipe thread bushing if you have a few minutes with a lathe as well - but I'd use square or hex bar stock to make it (so you'll have wrench flats to tighten the thing down...)
 
yeah thats what i looked for john, i guess i'll try a plumbing shop. I don't think using a ho cts is a good way to go, i'm assuming the voltage is not a match
 
Mike1331 said:
yeah thats what i looked for john, i guess i'll try a plumbing shop. I don't think using a ho cts is a good way to go, i'm assuming the voltage is not a match
Click to expand...

Most temperature sensors underhood are thermistors - resistors that vary their resistance in relation to temperature. They're used as current-varying devices, and the remaining current is what drives the gage.

However, I don't know the "response curve" for the CTS that drives the RENIX gage, so I can't tell you if the standard GM thermistor (used to report to the RENIX computer...) will work. However, the GM thermistor response curve is published in the FSM (under the CTS and IAT test procedures,) so you can check and see. If the values given per temperature (use your ohmmeter, a pot of water, and a thermometer to check) match with the thermistor response charts, you can probably then use a GM standard gage driver to drive the RENIX gage (it wouldn't surprise me to find out this was so, but I haven't had a chance to verify it experimentally...)
 
Mike1331 said:
interesting, i'll perform those test if i can't find the proper adapter. Thanks john
Click to expand...

Do you have the chart in an FSM, or should I find it for you? It's not a linear response curve, which is funny (and why I'm not sure it would work as a gage driver.)

But, I'd appreciate confirmation either way, if you check it out.
 
Johnnie Walker said:
Um, try and splice the current wire for CTS into the one on the t-stat housing.
Click to expand...
May be a good idea, may not. AFAIK some sensors are ground referenced and some are +12 referenced and some others are +5 referenced, so I would worry about the two temp sensors expected signals being different. I suspect the one on the t-stat housing is +12 referenced but don't have my schematics with me atm, and I am pretty sure the other one is a one-wire ground referenced sensor.
 
the CTS sensors for RENIX and HO use different resistance curves

Lowes has an adapter in the plumbing aisle that will let you use the block drain plug. Here is a pic of a temp gauge sender in the adapter. Take the CTS with you

Coolant_Sender_Drain_Plug.sized.jpg


You should also try to rig up a wire loom in the thread bung to the rear of the drain--the exhaust temp down there is super high and melts wires fast.
 
ehall, my renix block already had a temp sensor in that spot. That spot in my 99 block is currently being used by the renix cts. The cts going to the back of the cylinder head is the one i'm having issues with. I wana say it only has one wire coming out of it but i'll have to double check when i get home tonight.

John, i do not have the schematics.
 
Why not use your 7120 head on the 99 block?
 
Slip Kid said:
Why not use your 7120 head on the 99 block?
Click to expand...

I could but my 99 long block only has 77k miles on it. Plus i'd have to buy a new head gasket and head studs, which i really don't have the money for at the moment. I'm looking for the quickest possible route to get this pos going for a trip to the dunes/reno for new years.

The 7120 head was resurfaced, rebuilt and had a valve job done on it about 15k miles ago but its probably best to let an engine decay as a whole unit. I found that out the hard way after putting this fresh head on a tired and scored lower end.
 
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CTS--coolant temperature sensor, feeds data to the ECU/PCM.

Temperature gauge/idiot light sender for the gauge.

Renix gauge calibration: 1365 ohms = 100 F; 93.5 ohms = 220 F; 55.1 ohms = 260 F

Go to NAPA, they should be able to look up a 1/8 NPT sender with those values.

As 5-90 stated, you will be getting a slightly "cooler" reading at the thermostat housing, but I don't know by how much.

You can also get upper/lower radiator hose pipes with bungs, as well as heater hose pipes too.
 
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